Thigh Flab Healthier than Muffin Top

By Karen Rowan, Health Editor |
October 4, 2010 09:32am ET

MORE

Some people who are overweight or obese are metabolically healthy, while
others are plagued with high blood pressure, problems regulating their
blood sugar and high levels of fats in their blood. A new study shows
the difference between these groups may be linked to the site of fat in
the body.

When people gain fat in their thighs, their bodies typically produce new fat cells, whereas gaining fat in the abdomen usually involves an expansion of existing fat cells, according to researchers at the Mayo Clinic in Rochester, Minn.

The research upends previously held theories that the bodies of
adults are largely incapable of producing new fat cells, and weight gain
simply causes existing fat cells to swell, said study researcher Dr.
Michael Jenson, an endocrinologist at the Mayo Clinic.

Fat cells provide a useful service to our bodies by storing fat in
confined areas and keeping it out of other cells, such as muscle or
liver cells, where it can be harmful. Some overweight people have "healthy" fat
tissue that behaves the same way fat tissue in lean people behaves,
Jensen said, they just have more of it. In others who are overweight,
the fat is behaving in an unhealthy manner.

"Our findings suggest that this may be because lower-body fat gain is
largely the result of gaining more fat cells, each able to function
normally, as opposed to the fat cells becoming so big they no longer
store and release fat normally," Jensen said.

"People gained a lot of new cells, even without that much weight
gain," Jensen said. A gain of about 3.5 pounds (1.6 kilograms) of fat on
the thighs meant that about 2.6 billion new fat cells were created for
adult participants in the study.

Those who gained more of their weight
in their abdomens instead of in their thighs were less likely to
produce new fat cells. Instead, their gain came mainly from the
expansion of existing cells, Jensen said. Still, some did create new
abdominal fat cells, he said.

Losing weight
seems to improve the function of fat, he said. But if scientists
understood why fat behaves in such different ways, they may be able to
develop treatments that coax fat into behaving in a more healthy manner.

The researchers based their findings on 28 people, most of whom were
in their 20s, Jenson said. The participants overate for eight weeks, consuming candy bars, milk shakes and almost anything else they wanted to eat.

Seeking to understand why some people gain weight in their thighs
while others pack extra pounds into their abdomen, the researchers
measured the amount of fat in these regions, and the number of fat
cells. On average, the participants gained 5.5 pounds (2.5 kilograms) in
their upper bodies, and 3.3 pounds (1.5 kg) in their lower bodies.

People varied greatly in terms of where the weight went, Jensen told
MyHealthNewsDaily. Some gained most of it in their abdomen and just a
little in their thighs, while others saw the opposite happen.

"We thought for sure we'd see that women gained more weight in their
thighs," he said, however, the study did not find any differences
between men and women in terms of where the weight went, Jensen said.
But the results may be different in older men and women, he added.

The researchers studied the characteristics of fat cells — their
genes, cellular chemistry and the ways they interacted with hormones —
trying to find the reason fat tended to accumulate in one site or the
other, but the cause remains elusive.

They did find some differences in levels of expression of some genes
in fat cells in the abdomen that were associated with whether fat cells
there grew in number or swelled in size.

Still, "none of the things we looked at was a good predictor of where the weight went," Jensen said.

Future studies will look further into the underlying causes of this, he said.

The findings are published today (Oct. 4) in the journal Proceedings of the National Academy of Sciences.

Karen came to LiveScience in 2010, after writing for Discover and Popular Mechanics magazines, and working as a correspondent for the Journal of the National Cancer Institute. She holds an M.S. degree in science and medical journalism from Boston University, as well as an M.S. in cellular biology from Northeastern Illinois University. Prior to becoming a journalist, Karen taught science at Adlai E. Stevenson High School, in Lincolnshire, Ill. for eight years.